The present invention relates to a platinum alloy electrocatalyst having an ordered structure which can be suitably employed in a phosphoric acid type fuel cell.
A platinum alloy catalyst employed as a cathode catalyst of a phosphoric acid type fuel cell (hereinafter referred to as PAFC) having a higher oxygen reduction activity than that of a pure platinum catalyst has been developed, and for attaining the further durability the development is directed to a platinum alloy catalyst having an ordered structure. Although a Pt-Ni-Co catalyst is well known in prior publications to exhibit a high oxygen reduction activity, no description can be found that the Pt-Ni-Co catalyst possesses the ordered structure. While several ordered catalysts have been proposed, the Pt-Ni-Co catalyst is not suggested to have an ordered structure.
Since a catalyst for a fuel cell is generally employed in 100% phosphoric acid at a temperature from 190.degree. to 210.degree. C., dissolution of alloy particles and decrease of a surface area of a metal due to sintering occur to accelerate deterioration of the performance. In order to overcome these disadvantages, a catalyst for a fuel cell with a higher oxygen reduction activity and a high durability is requested.
In order to respond to this request, a certain ordered alloy (for example, a platinum-iron-cobalt-copper alloy catalyst) has been proposed (U.S. Pat. No. 4,711,829). The present inventors have investigated various platinum alloy catalysts with an ordered structure which possess less dissolution of metals, less surface area decrease and more durability than the above four element catalyst to reach the present invention.